It is desirable for laundry detergent manufacturers to incorporate both hueing dye and brighteners into solid laundry detergent compositions, for example to provide benefits across a broader range of fabric typess and under a variety of different light conditions.
Deposition of hueing dye onto white fabric, yields the consumer perception of increased whiteness, and counteracts the fading and yellowing of fabrics.
Optical brighteners typically absorb invisible light such as ultraviolet light, and emit this energy as light. For the purpose of detergent products, the light is typically emitted in the visible spectrum, typically blue or green light. The extra emission in the blue and/or green range of the spectrum makes fabrics or textiles washed with detergent comprising brightener appear brighter to the human eye after washing. There are many detergent powders available in the market comprising various brightener molecules.
One problem of the brighteners is that they tend to exhibit low solubility and decreased dissolution rates in cold water. Modern day consumers are interested in washing in cold water for the energy savings and environmental benefits, but are hesitant to trade off the performance of brighteners by washing in cold. Modifying the particle size of the brightener and/or the crystalline form of specific brightener, such as C.I. fluorescent brightener 260, can lead to an increase in its dissolution rates, especially in cold water. For example, C.I. fluorescent brightener 260 having a weight average particle size in the range of from 3 to 30 micrometers show greater dissolution rates than brighteners of larger particle size. Additionally, the alpha crystalline form shows greater dissolution rates than the beta crystalline form.
Another problem of brighteners is that they are generally fabric specific. Some brighteners work well on cotton but not polyester and vice versa. There is a need to provide a detergent composition having good brightener performance on a wide variety of fabrics including both cotton and polyester fabric types.
However, when both hueing dyes and brighteners are incorporated into solid laundry detergent compositions, the performance of the brightener can be negatively affected by the presence of hueing dye. The Inventors have found that by combining specific brighteners with specific hueing dyes, this negative interaction between hueing dye and brightener is not only mitigated, but a synergistic effect on increased brightener performance is observed
The Inventors have found that the combination of specific hueing dyes, referred to herein as bluing agents, as defined in the present invention, and specific brighteners, as defined in the present invention, lead to an increase in the whiteness of a set of fabrics having different fabric types with greater efficacy than when either technology is applied independently: the specific bluing agents maximize the synergy with the specific brighteners. By utilizing the combination of specific bluing agents and specific brighteners, the life of the textile substrates, such as clothing articles, table linens, etc., may be extended.